The major objective of this contract will be to maintain a repository for the production, maintenance, and distribution of aneuploid mice with a primary emphasis on trisomy 16. In addition, special emphasis shall be made on the production and characterization of single gene transgenics and YAC or BAC transgenics utilizing segments of human chromosome 21. More specifically, the contractor will perform detailed phenotypic characterization of the Ts65Dn mouse and another partial trisomy, T232Dn while developing new transgenic mice carrying either single or multiple human chromosome 21 genes. All of the mice produced and those currently in the Repository shall be distributed to the research community.